Blade platform with friction damping interlock

ABSTRACT

A turbomachinery rotor blade for disposition within a fluid flow path in cooperation with a rotatable disc is provided with a platform for partially defining the flow path of the fluid. The platform is disposed between the airfoil of the blade and preselected means for mounting the blade to a rotatable disc. The platform is provided with means for resisting circumferential and radial vibratory displacement by the action of frictional damping. The damping is supplied by frictional engagement with platforms of laterally adjacent blades. To enhance this function, the circumferential extremities of the platforms are provided with two diagonal edges axially spaced from one another along the same axial line, the edges having predetermined angular offsets from the radial direction. The two edges along each circumferential extremity have anuglar offsets of opposite senses, and adjacent platforms effectively interlock with one another.

United States Patent 1191 1111 3,923,420

Chifos 1 1 Dec. 2. 1975 BLADE PLATFORM WITH FRICTION 3,801,221 4/1974Zlotek 416/216 DAMPNG INTERLOC FOREIGN PATENTS 012 APPLICATIONS 1 1lnvemori Paul Chifos, Cincinnati Ohio 1.374.917 8/1964 France 416/191[73] Assignee: General Electric Company,

Cincinnati, Ohio Primary Examiner-Everette A. Powell. Jr. Filed: p 30,1973 Attorney, Agent, or Firm-Henry J. Pol1c1nsk1; Derek P. Lawrence[21] Appl. No.: 355,772

[57] ABSTRACT [52] US 416/190; 416/193; A turbomachinery rotor blade fordisposition within a fluid flow path in cooperation with a rotatabledisc is [51] 1nt.Cl. ..F01D 5/10 mvided with a latfo for lama d fininthe flow [58] FieldofSearch ..416/191,212A, 193, 190, p p Tm e g 416/215216 196 500 path of the flLllCl. The platform 1s disposed between theairfoil of the blade and preselected means for mount- [56] ReferencesCited mg the blade to a rotatable dilSC'. The platform 13 prov1ded w1thmeans for resIstIng c1rcumferent1al and ra- UNITED STATES PATENTS dialvibratory displacement by the action of frictional 2,398,140 4/1946Heppner 416/216 damping, The damping is supplied by frictional en-21772354 12/1956 416/190 gagement with platforms of laterally adjacentblades, 2805838 9/1957 F 416/216 X To enhance this function. thecircumferential extremi- 2,955,799 /1960 O1ckle 416/193 UX ties of theplatforms are rovided with two dia Onal 2,999,631 9/1961 Wollmershauser.416 191 d n d f P h g 3.014 12/1961 Rankin et al. 416/191 8 5 9 Y Spaceanothe? along I 6 same 3,104,093 9/1963 Craig et a1 416/ X axial lme,the edges haymg predetermmed angular off. 3,216,700 11/1965 Bostock 1416/216 Sets from the radlfll dlrectlon- The two edges along 3,307,7753/1967 Petrie 416/193 UX each circumferential extremity have anuglaroffsets of 3,396,905 8/1968 Johnson I 416/190 X opposite senses, andadjacent platforms effectively in- Williamson terlock one another3,761,200 9/1973 Gardiner 416/193 X 3,795,462 3/1974 Trumpler 416/196 6Claims, 7 Drawing Figures US. Patent Dec. 2, 1975 BLADE PLATFORM WITHFRICTION DAMPING INTERLOCK The invention herein described was made inthe course of or under a contract, or a subcontract thereunder, with theUS. Department of the Air Force.

BACKGROUND OF THE INVENTION The present invention relates to blades foruse in turbomachinery and, more particularly, to frictional vibration-damping systems therefor.

For the purpose of defining an aerodynamically efficient flow path forthe working fluid within a gas turbine engine, airfoil blades areprovided with platforms which combine with abutting similar platforms ofadjacent blades to separate the fluid flow path from associated rotorcavities. High-speed rotation of rotor blades combines with theimpingement upon the platforms and associated airfoils of a moving fluidto produce vi brational excitation which can do severe damage to theblade. More particularly, certain of these excitations may createvarious vibrational modes within the aforementioned platforms which canresult in the dismemberment of the platforms by the breaking off ofportions thereof.

Particularly susceptible to such breakage are the angular corners ofplatforms of typical design. Elimination of such angular corners mightprovide assistance in solving this problem. However, aerodynamicefficiency requies a substantially cylindrical path definition in thisarea which, when translated into terms of adjacent abutting platformsrequires such angular corners.

Other damage to the rotor blades through vibration can occur. Forexample, certain modes of vibration often result in damage to portionsof the airfoil surfaces thereof by breakage and loss of corners or bycracking and splitting in various directions. All of this vibrationaldamage is harmful to the useful life of the blades and is thereforeadvantageously eliminated.

Prior attempts at eliminating such vibration has included attempts totune resonant frequencies of the various vibrational modes within theblades in order to remove them from the operating regime of the engine.These attempts have been successful to only a limited extent for thereason that such engines are operable within a wide range with theresult that certain resonant frequencies cannot be eliminated. Inrecognition of this problem, prior attempts have been made to damp theamplitudes of vibrations which remain within operating ranges.

Damping has commonly taken the form of frictional engagement of aportion of the blade by a member added for that purpose. In particular,one prior attempt has involved the circumferential lengthening of bladeplatforms and the further addition of circumferentially extendingoverlapping plates between blades which members cooperate to dampvibrational amplitudes. Unfortunate characteristics of this and similardevices include the weight and expense required in the addition ofelements which serve no function other than damping. Furthermore, lackof an effective interlock between blades and engaging dampers allows thedamping elements to become separated over extended use with thepossibility of no longer performing their damping function.

The present invention remedies these and other objections to bladedamping members of the prior art by the provision for an interlockingblade platform which performs efficient frictional damping without thene cessity of increasing the weight or size of the platform.

The invention relies, in part, upon recognition that, since typicalblade airfoils are mounted substantially diagonally of the bladeplatforms, the corners proximate the leading and trailing edges of theairfoil will be stiffened thereby and experience vibrational amplitudessubstantially lower than the unreinforced corners remote from theairfoil.

BRIEF SUMMARY OF THE INVENTION It is therefore a primary object of thepresent invention to provide a frictional damping system forturbomachinery rotor blades which effectively damps vibrations whilemaintaining an effective interlock for reliable extended use and whichdoes not necessitate the addition of costly and heavy materials toperform this function.

In order to accomplish this and other objectives, which will becomeapparent from the detailed description which follows, the presentinvention provides a rotor blade having a laterally extending platformdisposed along its length between its diagonally disposed airfoil andthe means for mounting the blade upon an associated rotor disc. Theplatform has a circumferential extremity disposed to either side of theairfoil, and this extremity is provided with diagonal edges which arecanted from the radial direction by predetermined angles. Each extremityhas two such edges, the aforementioned angles of which are of oppositesense. The diagonal edges of each platform are positioned to engage inan interlocking abutting relationship opposed edges of adjacent bladeplatforms. The edges thus formed provide frictional damping forvibration tending to cause relative radial motion between adjacentplatforms as well as relative circumferential motion therebetween.

BRIEF DESCRIPTION OF THE DRAWING The present invention will become moreeasily understood upon reading the following detailed description incombination with the appended drawing wherein:

FIG. I is a perspective view of a plurality of rotor blades according tothe present invention in their operating position upon an associateddisc;

FIG. 2 is a perspective view of an individual rotor blade according tothe present invention;

FIG. 3 is a top view of a rotor blade according to the presentinvention;

FIG. 4 is a side view of such a blade;

FIG. 5 is a cross-sectional view along line 55 of FIG. 1;

FIG. 6 is a cross-sectional view along line 66 of FIG. I andillustrating cooperation between opposed platform edges of adjacentblades, and

FIG. 7 is a view similar to that of FIG. 6 but illustrating cooperationbetween different platform edges.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT Referring to FIG. 1, arotor designated generally by the numeral 10 is shown to include arotatable disc 12 carrying a circumferential groove 14 in the peripherythereof which is adapted to receive and retain dovetail mounting means16 by which the individual blades 18 are attached to the disc. Thisparticular variety of disc includes a loading slot 20 for accommodatingthe blades within the groove 14 of the disc 12. The dovetail 16 extendsradially into conjunction with a platform 22 of each blade, whichcombines with adjacent platforms to partially define a fluid flow path23 within the engine and to which the present invention particularlypertains. Extending radially outwardly from the platform is an airfoil24 which is particularly configured to cooperate efficiently with a.fluid stream directed therepast.

In operation, this rotor functions substantially similarly to typicalrotors of this variety in that the disc 12 is attached to a shaft (notshown) about which it rotates in response to the interaction of thefluid stream with the blades 18 or in response to torque applied to theshaft by similar blades elsewhere disposed (depending upon whether theblades 18 shown are part of a turbine or a compressor). At any rate, theairfoils 24 of the various blades serve to transmit energy between disc12 and the fluid stream. During this process, the rotational velocity ofthe blades, as well as aerodynamic disturbances within the fluid flow,create vibrations of various frequencies which tend to excite the bladesat various frequencies. As mentioned hereinabove, such excitation may beundesirable since damage to the airfoils, platforms or other bladestructure may result. In order to reduce the destructive amplitude ofresonant frequencies in the blade material, which cannot be tuned out ofthe operating range of the engine, the present invention provides forfrictional damping between adjacent blade platforms 22.

Referring to the remaining figures, the particular configuration bywhich this damping is accomplished is disclosed. It can be seen thateach platform 22 includes two lateral extremities 30 and 32,respectively, which are provided with interlocking as well as dampingmeans which will be described hereinafter. The platform also includes anupstream end 34 and a downstream end 36.

The platform of the present invention includes both radial damping meansfor frictionally damping radial relative movement between adjacentplatforms, and circumferential damping means for frictionally dampingcircumferential relative movement between adjacent platforms. Generallythese damping devices depend upon engagement by each platform with theplatform of the circumferentially adjacent blade. To this end, eachplatform extends circumferentially outwardly of each airfoil and intosubstantial abutment with the adjacent platforms.

To enhance damping as well as to provide an effec tive interlock betweenplatforms, the present invention provides unique treatment for eachcircumferential extremity 30 and 32 of each blade 18. More particularly,extremity 30 can be seen to include a first diagonal edge 40 whichcomprises a surface disposed at an angle 6 I from the radial direction,as represented by line 41. In addition, extremity 30 includes a seconddiagonal edge 42 which is comprised of a canted surface offset by anangle 2 from the radial direction. It can be seen that angles 0 l and 492 are of the opposite sense.

For simplicityof manufacture, diagonal edges 40 and 42 lie axiallyupstream and downstream relative to one another and substantially alonga common axial line. (However, a similar arrangement might be madewherein the edges are radially spaced from one another and engageopposed edges of adjacent platforms.) It can also be seen that in thepresent embodiment, the extremity 30 is divided approximately intohalves axially by the presence of the diagonal edges with the first ofthe halves comprising the edge 40 and the second of the halvescomprising the edge 42.

Referring now to the second circumferential extremity 32, it can be seenthat this extremity incorporates a similar pair of diagonal edges 48 and50 which are canted from a radial line 52 by angles 6 3 and 0respectively. These angles are respectively of the same sense as areangles 6 1 and 0 2 stated above. In the present embodiment it can beseen that angles 0 0 0 3 and 6 4 are all substantially equal inmagnitude with one another. However, for proper functioning of theplatform this is not necessarily so. In order to achieve proper abuttingcooperation between the flat surfaces of the adjacent edges, angles 0 1and 0 3 are kept substantially equal, and angles 0 2 and 6 4 aresubstantially equal. Also, the surfaces of the diagonal edges 40, 42, 48and 50 may be provided with a frictionally enhanced surface to increasedamping, but this also is optional.

Thus described, the damping system of the present invention functions asfollows. Having been loaded by means of slot 20 into circumferentialgroove 14 and brought into abutting relationship with one another, theblades 18, according to the present invention, are retained within thegroove and rotate in unison upon rotation of disc 12. During operationof the gas turbine engine, the disc 12 rotates about an associated shaftas described hereinabove. Interaction between the airfoils 24 and theflow of fluid through the engine flow path 23 induces vibrations ofvarious frequencies, which are transmitted through the blade material tothe platform 22 of each blade. In addition, vibration induced to theblade dovetails 16 is transmitted through the blade material to theplatforms 22. Also the platforms may be excited directly by periodicfluid pressure fluctuations on the platform surface. As a result, theplatforms as well as the airfoils tend to vibrate in various modes.

As already indicated, the resonant frequencies of the blades are tunedout of the operating ranges of the engine to the extent possible.Nevertheless, certain of the resonant frequencies of the blades remainwithin the operating regime of the engine. The present inventionoperates to reduce the amplitude of such vibrations, as well as in someinstances to further tune the associated blades.

Typical vibrational modes can occur wherein the platforms 22 vibrate insuch a way that the platforms are placed in radial relative motion withrespect to adjacent platforms. Other vibrational modes might place theplatforms in circumferential motion relative to one another. The presentinvention functions to damp each of these relative movements by means offrictional energy dissipation.

As stated hereinabove, the blade platforms 22 are formed with fourcomers for the purpose of defining a relatively cylindrical and thusaerodynamically efficient fluid flow path. For example, in FIG. 3, thecorners are designated A, B, C and D. As further stated above, thosecorners of the blade platform which lie relatively closely to theleading and trailing edges of the airfoil 24 will be reinforced andstiffened thereby against steady state centrifugal as well as vibratorymotion. In the Figure, corners A and C exemplify such corners. On theother hand, the remaining corners, la-

present invention takes advantage of this characteristic by bringinginto abutment blade platforms in such a fashion that the reinforcedcorners A and C cooperate closely with mating unreinforced corners B andD of adjacent blades, and vice versa. As a result, vibration of eachcorner A, B, C or D of one blade platform meets with frictionalresistance provided by adjacent blade platforms.

More particularly, with reference to the present configuration, eachcorner A, a stiff corner, abuts a more flexible corner D of an adjacentblade, as shown in FIG. 6. Similarly, each comer C, a stiff corner,abuts a flexible corner B. Under the influence of a given vibratorystimulus, corners A and C will tend to vibrate with an amplitude smallerthan corners B and D. Hence, each corner, throughout its vibratorymotion will be rubbing against an adjacent corner having a differentamplitude of vibration. As a result, each corner tends to damp thevibration of its abutting mate and vice versa. This is the basicmechanism by which the present invention operates to effectively dampvibrational amplitudes, both in the radial and circumferentialdirections.

To further enhance this action, the stiff corners (A and C) areassociated with inwardly facing surfaces 48 and 42 respectively.Similarly, flexible corners B and D are associated with outwardly facingsurfaces 50 and 40. As a result, the steady state centrifugal force uponthe platform at any given RPM results in mating surfaces being broughtinto a more intimate contact, thus increasing the frictional dampingeffect of the present invention.

In addition, this mechanism is enhanced by the particular configurationof the blade platforms of the present invention. To this end, theinterlocking dual edges of each circumferential extremity 3t) and 32have been provided. As stated, the angles of departure of 6 1 and 6 3 ofthe surfaces 40 and 48, respectively, from the radial direction areequal in magnitude and of the same sense. Similarly, angles 2 and 6 4 bywhich surfaces 42 and 50 depart from the radial are also equal inmagnitude and of the same sense. As a result, when adjacent blades arebrought into abutment, surfaces 40 and 48 of adjacent blades overlie oneanother in substantially flush cooperation across their entire surfaces.The same is true of adjacent surfaces 42 and 50. The effect of thisconfiguration is, in part, to provide surfaces having frictionalengagement with one another both in the radial and circumferentialvibratory modes. In addition, the contacting surfaces vibrating in eachdirection are maximized in area to likewise maximize frictional force.Furthermore, the fact that each circumferential extremity incorporatestwo edges of opposite sense which engage two edges of likewise oppositesense of an adjacent blade provides for an interlocking mechanism forretaining the platforms against tendencies to separate from one another.This is a distinct improvement over prior art dampers which tend tobecome non-functional after lengthy service has resulted in materialdeformations. Another advantage of this configuration is that theinterlocking platform function minimizes the separation of adjacentplatforms under the influence of various vibrations and thus increasesdamping affect.

In addition to damping the amplitude of the various vibrations, thepresent invention offers means for further tuning the resonantfrequencies of the blades as may be desired. It is well known thatresonant frequency is a function of the mass in vibration as well as thespring constant associated therewith. Each platform involves apredetermined mass, a portion or all of which can be in vibration at anygiven time. In addition,

each platform incorporates a material and predetermined thickness whichjointlylead to the spring constant thereof. By bringing adjacent bladeplatforms into interlocking cooperation with one another, it is possibleto change the vibrating mass as well as the spring constant of the massin vibration without adding or subtracting material from the platformitself. More particularly, when a given portion of one platform isplaced in vibration and rubs against an adjacent platform tending todraw the adjacent platform into the same vibrational mode, the effectivemass in vibration may be greater or less than that where the firstplatform is not engaged by the second. Similarly, the spring constant ofthe two vibrating masses may be different and may supplement oneanother. These interactions may be utilized to adjust the resonantfrequencies of vibration of platforms utilizing the present inventionwhile the frictional damping means of these devices are used to reducevibrational amplitude as described hereinabove.

Thus may be described one embodiment of the present invention. It isreadily apparent that those skilled in the art may make substantialvariations of the structure presented herein without departing from thespirit of the present invention. For example, the particularconfiguration of the circumferential extremities of the present bladeplatforms may be varied substantially but their function maintained. Onesuch example was mentioned hereinabove wherein it was stated that theoppositely angled edges of one extremity might be radially displacedfrom one another rather than axially. Equalivantly, a tongue and groovecooperation might be es tablished between adjacent lblade platformswhich would serve to both frictionally damp the amplitude of vibrationsand partially tune the resonant frequencies thereof. Such variations areintended to be comprehended within the scope of the following claims.

What is claimed as new and intended to be secured by Letters Patent ofthe United States is:

1. A turbomachinery rotor blade for disposition within a fluid flow pathin cooperation with a rotatable disc, the blade comprising:

an airfoil;

mounting means extending radially from the airfoil for attaching theblade to the disc; and

a platform disposed between the airfoil and the mounting means, theplatform comprising first and second circumferential extremities andfirst means for abutting and interlocking said platform radially,axially and circumferentiallywith a similar adjacent platform topartially define the flow path and for frictionally damping radial andcircumferential relative movement between said platform and saidadjacent platform, said first means including first and second diagonaledges on said first extremity of said platform, said first diagonal edgebeing canted from the radial direction by a predetermined first angle,said second diagonal edge being canted from the radial direction by apredetermined second angle of opposite sense from said first angle, saidfirst and second diagonal edges positioned to abut and interlock with anedge of the adjacent platform in sliding frictional engagement therewithand further positioned to effect damping of radial and circumferentialrelative movement between said diagonal edges and said adjacent edgeduring said frictional engagement.

2. The blade of claim 1 wherein said first and second diagonal edges lieaxially upstream and downstream relative to one another.

3. The blade of claim 2 wherein said first and second diagonal edges liealong a substantially common axial line.

4. The blade of claim 3 wherein said first circumferential extremity isdivided approximately into halves axially, one of said halves comprisingsaid first edge,

and the second of said halves comprising said second edge.

5. The blade of claim 1 wherein said first means includes third andfourth diagonal edges on said second extremity, said second extremitybeing disposed to the side of the platform laterally opposite said firstextremity, said third diagonal edge canted from the radial direction bya predetermined third angle and said fourth diagonal edge canted fromthe radial direction by a predetermined fourth angle of opposite sensefrom said third angle.

6. The blade of claim 5 wherein said first and third angles aresubstantially equal and said second and fourth angles are substantiallyequal.

1. A turbomachinery rotor blade for disposition within a fluid flow pathin cooperation with a rotatable disc, the blade comprising: an airfoil;mounting means extending radially from the airfoil for attaching theblade to the disc; and a platform disposed between the airfoil and themounting means, the platform comprising first and second circumferentialextremities and first means for abutting and interlocking said platformradially, axially and circumferentially with a similar adjacent platformto partially define the flow path and for frictionally damping radialand circumferential relative movement between said platform and saidadjacent platform, said first means including first and second diagonaledges on said first extremity of said platform, said first diagonal edgebeing canted from the radial direction by a predetermined first angle,said second diagonal edge being canted from the radial direction by apredetermined second angle of opposite sense from said first angle, saidfirst and second diagonal edges positioned to abut and interlock with anedge of the adjacent platform in sliding frictional engagement therewithand further positioned to effect damping of radial and circumferentialrelative movement between said diagonal edges and said adjacent edgeduring said frictional engagement.
 2. The blade of claim 1 wherein saidfirst and second diagonal edges lie axially upstream and downstreamrelative to one another.
 3. The blade of claim 2 wherein said first andsecond diagonal edges lie along a substantially common axial line. 4.The blade of claim 3 wherein said first circumferential extremity isdivided approximately into halves axially, one of said halves comprisingsaid first edge, and the second of said halves comprising said secondedge.
 5. The blade of claim 1 wherein said first means includes thirdand fourth diagonal edges on said second extremity, said secondextremity being disposed to the side of the platform laterally oppositesaid first extremity, said third diagonal edge canted from the radialdirection by a predetermined third angle and said fourth diagonal edgecanted from the radial direction by a predetermined fourth angle ofopposite sense from said third angle.
 6. The blade of claim 5 whereinsaid first and third angles are substantially equal and said second andfourth angles are substantially equal.